As part of our continuing program on the study of the conformation of biopolymers and their model systems, we have investigated the conformational properties of substituted cyclic dipeptides. We have found that these compounds assume boat-like conformations in the solid state. We are at present extending the study to include the solution properties of these compounds with the object of deriving information concerning peptide hormone structure. In addition, we are examining acylated proline and proline-like amides. We have established that these compounds exist in the trans conformation. In the crystal, acetyl prolineamide shows a ring conformation in which the pyrrolidine is puckered at the beta-carbon atom while in acetyl thiazolidine-4-carboxamide the ring puckers at the gamma-carbon. Lastly, we are investigating the conformations of polydepsipeptides. We have found that poly(L-alanyl-L-lactic acid) is not ordered in solution even though our calculations predict two low-energy ordered conformations. We have commenced a study of poly(L-alanyl-L-alanyl-L-lactic acid). We expect that this material will exhibit ordered conformations in solution since our calculations show it to be a much more stable, ordered structure. BIBLIOGRAPHIC REFERENCES: M. Goodman, R.T. Ingwall and S. St. Pierre. Synthesis and Conformation of Sequential Polypeptides of L-Alanine and beta-Aminobutyric Acid. Macromolecules, 9, 1 (1976). W. Radding, N. Ueyama, C. Gilon and M. Goodman. Measurement of Circular Dichroism using a Thin Cell. Biopolymers, 15, 591 (1976).